Quiet-Sun hydrogen Lyman-alpha line profile derived from SOHO/SUMER solar-disk observations

Abstract

The solar radiation in the Lyman-alpha spectral line of hydrogen plays a significant role in the illumination of chromospheric and coronal structures, such as prominences, spicules, chromospheric fibrils, cores of coronal mass ejections, and solar wind. Moreover, it is important for the investigation of the heliosphere, Earth's ionosphere, and the atmospheres of planets, moons, and comets. We derive a reference quiet-Sun Lyman-alpha spectral profile that is representative of the Lyman-alpha radiation from the solar disk during a minimum of solar activity. This profile can serve as an incident radiation boundary condition for the radiative transfer modelling of chromospheric and coronal structures. Because the solar radiation in the Lyman lines is not constant over time but varies significantly with the solar cycle, we provide a method for the adaptation of the incident radiation Lyman line profiles (Lyman-alpha and higher lines) to a specific date. Moreover, we analyse how the change in the incident radiation influences the synthetic spectra produced by the radiative transfer modelling. To take into account the Lyman-alpha variation with the solar cycle, we used the LISIRD composite Lyman-alpha$ index. To estimate the influence of the change in the incident radiation in the Lyman lines on the results of radiative transfer models, we used a 2D prominence fine structure model. The analysis of the influence of the change in the incident radiation shows that the synthetic spectra are strongly affected by the modification of the incident radiation boundary condition. The hydrogen H alpha line can also be considerably affected, despite the fact that the H alpha radiation from the solar disk does not vary with the solar cycle.

17 pages, 7 figures, 2 appendices (A, B), to be published in Astronomy and Astrophysics

References in corpus (6)

• The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance
• The Ly-alpha profile and center-to-limb variation of the quiet Sun
• Hydrogen Lyman-alpha and Lyman-beta spectral radiance profiles in the quiet Sun
• IRIS Mg II Observations and Non-LTE Modeling of Off-limb Spicules in a Solar Polar Coronal Hole
• 2D non-LTE modelling of a filament observed in the H_alpha line with the DST/IBIS spectropolarimeter
• Stability of the interstellar hydrogen inflow longitude from 20 years of SOHO/SWAN observations

Cited by in corpus (3)

• Intrinsic Lyman alpha Profiles of High-Velocity G, K, and M Dwarfs
• Combining White Light and UV Lyman-alpha Coronagraphic Images to determine the Solar Wind Speed: the Quick Inversion Method
• Effects of the chromospheric Lyα line profile shape on the determination of the solar wind HI outflow velocity using the Doppler dimming technique